The present invention relates to a surveillance camera that is mounted onto a for-surveillance-camera rotary base capable of performing a pan (i.e., transverse oscillation) rotation and a tilt (i.e., longitudinal oscillation) rotation. Moreover, the surveillance camera is a one which, in order to protect privacy, includes a mask storage unit and a mask display unit for masking only a privacy-protected range photographed in part of an image.
In the surveillance camera, a video camera is fixed onto the for-surveillance-camera rotary base that is freely rotatable in the pan direction and the tilt direction. This surveillance camera is the following system: An external controller unit operates the for-surveillance-camera rotary base, zooming of the camera, and the like, thereby freely changing an image spot to be photographed by the camera. This surveillance system, in general, includes a sequence function for storing a plurality of image spots so as to project in sequence these stored image spots at a constant point-in-time, an alarm function that, if an unusual event happens, causes the camera to instantaneously direct toward that direction, and the like. Here, the alarm function is implemented by setting up a human-sensitive sensor or the like in a surveillance area. When setting up the surveillance system like this in public places such as a street, there exists a problem of dealing with such a spot as a private house that is undesirable to be photographed from the viewpoint of the privacy protection. As a solving method for this problem, there exists a one of masking, with another image, a spot that necessitates the privacy protection. Hereinafter, the explanation will be given below concerning conventional privacy masking methods.
In JP-A-6-181539, the following method has been described: A privacy-protected range is stored in advance by the central angles and the range widths in the vertical direction and the horizontal direction. Next, if division areas, which result from dividing an image output into M-row and N-column areas, overlap partially with the privacy-protected range, the division areas are masked. In this method, the image output is masked on the M-row and N-column division basis. This eventually masks the portion that need not be masked, thereby lowering the surveillance function. Also, the range to be masked is managed using the angles in the vertical and the horizontal directions. This causes a difference to occur between a rotation displacement of the photograph-target, which, as illustrated in FIG. 8B, is caused by the pan rotation near a location directly below or above the camera's direction, and vertical and horizontal displacements of the mask. As a result, there exists a problem that the mask deviates from the privacy mask.
In JP-A-2001-69494, the following method has been described: The privacy-protected range is stored in advance by the coordinates on the absolute coordinate system, the size thereon, or the like. At the time of displaying the mask, the absolute coordinate system is converted into the picture coordinate system, then causing the mask to be displayed. In this method, a tilt angle at which the camera's direction is directed toward near a location directly below or above the camera-mounted position, the rotation displacement of the photograph-target becomes larger, and accordingly the masking exhibits no significant effect. On account of this, the above-described method has applied no masking near the location directly below or above the camera-mounted position where the rotation displacement becomes larger. Also, when setting up the privacy-protected range, the masking exhibits no significant effect on photograph-targets which, as illustrated in FIG. 8A and FIG. 8C, exist at the picture edges and thus whose images have been distorted. On account of this, the method has set up the privacy-protected range at the picture center.